Flavonoids Mediate the Modulation of Phosphate Uptake and Phosphate-Starvation Signaling in Tobacco

Phosphorus (P) is an essential macro-nutrient for plant growth and development, and inorganic phosphate (Pi) is the primary form of P taken up by plants. Previous studies have shown that P deficiency influenced the accumulation of flavonoids in plants. However, the mechanisms underlying the interplay between P nutrition and flavonoid accumulation are still largely unclear thus far. In this study, we adopted tobacco plant ( Nicotiana tabacum ) to study how P nutrition regulates flavonoid biosynthesis and also to investigate whether application of certain flavonoids may in turn influence Pi uptake. We found that P deficiency increased the accumulation of total flavonoids in tobacco shoots, but not in roots, and the transcripts of four genes, NtCHS, NtF3H, NtDFR, and NtFLS , which are involved in flavonol biosynthesis, were significantly increased in leaves under P deficiency. Consistently, the NtCHS promoter could drive a much higher expression level of the GUS (β-Glucuronidase) reporter gene in tobacco leaves treated with low Pi than those treated with high Pi. External application of the flavonol, quercetin, reduced the soluble Pi concentration, but enhanced the Pi-starvation response in tobacco roots. Application of quercetin also weakened the DR5-GUS activity, a reporter for auxin response, in tobacco roots treated with low Pi. RNA sequencing analysis revealed that multiple genes encoding the putative Pi transporters and purple acid phosphatases were up-regulated in tobacco roots by quercetin application. Our results proposed that P deficiency promotes flavonoid biosynthesis in tobacco leaves, and flavonoids could also mediate the regulation of Pi uptake and Pi-starvation signaling, probably via the auxin signaling pathway.